grinding noise

i recently purchased a 94 ram 1500 2wd slt there is a wierd grinding sound coming from under the truck while driving it dosnt increase with speed it dosnt do it in neutral or when im stoped if im driving it stays the same but if i let off the gas pedal it gets louder but not faster if i put my foot back down it goes back the way it was

please give me an idea

i recently purchased a 94 ram 1500 2wd slt there is a wierd grinding sound coming from under the truck while driving it dosnt increase with speed it dosnt do it in neutral or when im stoped if im driving it stays the same but if i let off the gas pedal it gets louder but not faster if i put my foot back down it goes back the way it was

please give me an idea

Have you looked at your u-joints?